Wood preservative composition



United States Patent This invention relates to wood preservative compositions suitable for treating wood poles, e.g. electric power lines or telephone wood poles to provide protection against insects, fungus, rot, etc. Particularly, the invention relates to a wood preservativecomposition comprising mineral oil thickened to a grease-like consistency with a finely divided silica and containing one or more wood preservatives.

The grease-like compositions of the invention can be brushed, or applied with a trowel, to poles already in place. The grease-like consistency of the composition holds the composition in place on the pole while the oil and wood preservative components gradually seep into ,the' wood pole to provide the required protection.

Generally about 0.15 to 0.5 inch penetration of the :WQOd pole by the wood preservative is'desired. If the penetration is less than this, then the number of years of effective protection is greatly decreased as the pole ages. Thus, as time passes, the treated pole surface gradually loses the preservative composition through weathering, leaching of preservative from the pole by rain water, and the effect of sunlight in providing oxidation in the portion above ground level.

The desired degree of penetration can generally be obtained by coating the poles with a coating about A" thick, of the compositions of the invention. Then over a period of about one to four days, the oil, carrying the dissolved or dispersed wood preservative components, will bleed into the wood to .give the desired degree of penetration. The coating of the invention can be applied either before or after the poles are set in their permanent position. However, the composition is easier to apply after the pole 'is set in its hole, but before the hole is filled in with earth. Frequently, new unset poles will betreated to coat their underground portion and a short portion extending above the ground.

Certain low viscosity ieral oil fractions, preferably aromatic, such as low viscosity highly aromatic gas oil will give thedesired amount of penetration into the wood so as to carry the dissolved wood preservative the desired distance into the wood. By thickening the dispersion or solution of preservative in low viscosity oil, with a silica thickener, the desired grease-like consistency and structure "stability can be obtained so that the composition will not unduly slurnpor run off when applied to a pole. At the same time, the silica thickeners'of the invention do not unduly interfere with the wood penetration, and only relatively small proportions of said silica thickeners are required to thicken the oil solution to the desired consistency. On the other hand, if the gas oil solution of preservative is thickened with more conventional thickeners such as soap, e.g. aluminum stearate, the soap will 5 unduly dissolve in the aromatic oil fraction- Thus, because of its highe-r oil solubility, larger amounts of soap thickener would be required to obtain the desired grease like consistency. Also structural stability is very poor with soap-thickened low viscosity oils. Attempts to thicken the oil solution of preservative to a grease consistency with various -waxes was unsuccessful since the wax tends to fill the pores of the wood to thereby prevent penetration by the oily component carrying the preservative. Thickening the oil solution of preservative with to the desired final oil viscosity. ltroleum tars and' asp'halts have many components which 30 3,132,071 Patented May 5, 1964 ice clays, generally results in a blend which is very difiicult to manufacture coupling agents, wetting agents and milling is usually required. Also, relatively large concentrations of the clay thickener (e.g. 10 wt. percent and more) are generally required since the particle size of most commercial clays, e.g. bentonite type clays such as B-aragel, is about 0.8 micron. 'Furthermore, the usual needle-shaped particles of many clays are believed to behave somewhat as wax crystals blocking the pores of the wood, thereby making wood penetration more difficult by the oil solution of the wood preservative.

The preferred mineral oil fraction used to form the compositions of the invention is gas oil, which is generally derived by distillation of cracked petroleum crude. Gas oils are low viscosity oils boiling the range of about 350 to 750 F. and can be thought of as the fraction between kerosene and lubricating oil. The preferred gas, oils will have viscosities of about 20 to 40 SSU,

preferably 30 to 38 SSU at 100 F. Gas oils high in aromatics, e.g. to wt. percent aromatic, are especial- -ly preferred becauseof their'higher solvency power for it is frequently desired that the oil component have a slightly higher viscosity than the less viscous of the gas oils. It has been found that petroleum tars or 'asphalts can be used to slightly thicken the lower viscosity gas oils Furthermore, such peare similar to the components of coal tar creosote and which are believed to have wood preservative properties in themselves. The final oil will generally have a viscosity of 30 to 40, preferably 32 to 38, SSU at 100 F. and

can be obtained by using :gas oil having a viscosity in the desired range or by using gas oil with 1 to 25 wt. percent of asphalt or tar.

'Ihe silica thickening agent of the invention will consist of finely divide silica particles having particle sizes of about 0.01 to .050, preferably 0.015 and 0.030 micron.

These finely divided silicas can be obtained by condensation of silica fuines obtained byburning SiCL, as described in a paper by Kenneth A. Loftman which was presented to the Division of Colloid Chemistry at the 13th National Meeting of the American Chemical Society, April 14, 1960. This method is carried out as follows: Essentially pure silicon tetrachloride is vaporized and transported to a furnace in which a hydrogen flame burn-s (-1100" C.) The water vapor producedcn combustion reacts with the $01.; to give SiO and HCl. The adsorbed HCl is driven off by heatand steam in a calcium and the finely divided SiO is recovered. A particular silica produced by the aforesaid method and used in the working examples of the invention is commercially available from Godfrey L.

Cabot Inc. of Boston, Massachusetts underthe name of Cab-O-Sil. This silica has particle sims ranging from about 0.02. to 0. 025 micron, and a bulk density of about to 5.0 lbs/cu. ft.

The wood preservative canbe any of a: large number of well known oil-soluble wood preservatives. The most common woodpreservatives :are highly chlorinated aro matic hydrocarbons and phenols, such as pentachlorophenol. Other common; wood preservatives include coal tar creosote, petroleum oil creosote, wood creosote, petroleum tars, copper. naphtheuate, etc. Also, finely divided oil-insoluble materials can be used, such as borax, as supplementary wood preservatives.

The finished wood preservative compositions of the invention will comprise a major amount of low viscosity oil, a grease thickening amount of such a 4 to 8 wt. percent of a finely divided silica, and a wood preserving amount such as about 5 to 35 wt. percent of the wood preservative. Preferred compositions will comprise about 5 to 7 wt. percent of a silica and about 10 to 25 wt. percent of wood preservative. Especially preferred compositions will have a woodpreservative comprising pentachlorophenol and steam cracked tar. i 5 The compositions of the invention are readily made by sirnple mixing of the silica thickening and the wood preservative into the oil medium to form a grease-like mass, which can subsequently be applied by brushing or r by spatula to the wood pole. 1()

EXAMPLE I A series of compositions were prepared using various blends of a steam cracked gas oil and a steam cracked petroleum tar. The physical characteristics of these two materials are summarized in Table I which follows: 15

-T able I Gas Oil Tar 2 Gravity, API 14. 5 4. 7 Flash, 000. 150 Visc. at 100 it, sets. 32.3 Vise. at 210 F., SUS 250 FIA Aromatics, vol. percen 85-93 90 FIA Olefins, vol. percent... Pour Point, F ASTMpDist-illation, F.:

penetration or complete penetration.

The specific compositions tested and the results obtaincd are summarized in Table II which follows:

Table II 50 EFFECT OF OIL VISCOSITY ON WOOD PENETRATION CHARACTERISTICS Formula, percent by wt.:

Steam Cracked Gas 011.--- 30 50 6O 70 80 90 95 Steam Cracked Tar 70 50 40 30 20 10 5 55 Inspections:

Vise. at 100 F., SSU 400 85 56 44 38 34. 5 33. 3 Penetration of Wood, percent 5 5 5 50 100 100 100 The preceding table illustrates the importance of a low viscosity of the oil in order to obtain good penetration. 'In .generaL'viscosities at 100 F. of 32 to 38 SUS. will give the desired degree of wood penetration.

' A series of compositions, A to D, representing the invention were prepared using the aforesaid gas oil and cracked tar with Cab-O-Sil as the silica thickener. The compositions were prepared by stirring the gas oil, tar and pentachlorophenol while heating at 175 F. The

mixture was then allowed to cool to about 100 R,

where the Cab-O-Sil was stirred in to form a thickened mixture; Then, finely divided boraX Was added to the thickened mixture. Th-e'borax was added last to prevent settling since it islinsoluble in the composition.

The resulting compositions were tested for slumping by coating the upper "half of a wood panel measuring 2%" x 6" x A" with a A" thick layer of the test compound. The panel is then held vertically at room temperature (77 F.)'for about hours. Slumping of the test compound during the 15 hour period of more than a fourth of an inch indicates failure. Penetration was measured by coating x sq. sticks of jack pine sapwood witha A" layer of the test composition, then leaving the treated wood panel set for 4 days at room temperature. Next, the outer surface of test compound is removed and the panel is sawed in half to determine the extent of penetration. The penetration is reported in percent penetration. Thus 50% penetration indicates inch penetration; 75% penetration indicates inchpenetration and 100% penetration is inch penetration from the outer surface.

For comparison, compositions E to G consisting of gas oil, cracked tar and Cab-O-Sil were also prepared.

The compositions tested and the results obtained are summarized in Table III, which follows: 7

Table III Composition Formula, percent by wt.

A B C D E F G I 340 528 Steam Cracked Gas on. as 60 417 574 Steam Cracked Tar 14 10 429 595 Cab-O-Sil 6 6 444 627 Pentachlorophenol. .10 10 455 660 Borax. 14' 14 40%. 464 694 30 Inspection: 1 473 7: Viscosityofoilpor- 483 8 7 tion at 100 F-, 493 ssU 3s 36 34.5 33.3 56 44 38 506 Slump Test pass pass pass pass pass pass pass 32% Penetration of FBP 555 Wood, Percent.-- 50-75 50-75 5 50-75 As seen by Table 111, compositions A to D of the invention were satisfactory with'regard to slumping and penetration, although compositions C and D were particularly satisfactory because of their higher penetration. Thus, composition A showed penetration ranging from to inch, i.e. 50 to 75 penetration. While 100% penetration is of course the most desired, lesser penetrations are acceptable since the slower penetration can generally be otfset by letting the composition remain on the wood surface a. longer length of time and/or by using a heavier coating of the :composition on the wood surface. These compositions all had consistencies similar .to that of a soft grease. For example, composition C had an ASTM cone penetration measured in a grease penetrome'ter of 330 mm./ 10 at 77 F.

Compositions E to G contained no wood preservative and are presented primarily for the purpose of demonstrating the necessity for the final oily portion to have a relatively low viscosity in order to obtain good penetration.

What is claimed is:

1. A grease-like wood preservative composition consisting of a major amount of an oil blend having a viscosity of '30 to 40 SSU at 100 F., which consists of gas oil containing in excess of 80 wt. percent aromatics and having a viscosity of 20 to 38 SSU at 100 CR, and steam-cracked petroleum tar; 4 to 8 wt. percent of silica having particle size of 0.015 to0.030 micron; and 5 to 35 wt. percent of a wood preservative.

2.;A composition'according to claim 1, wherein said wood preservative consists of about 10 wt. percent pentachlorophenol and about 14 wt. percent borax.

3. A grease-like wood preservative composition consisting essentially of a major proportion of a mineral oil having a viscosity ofabout 30 to 40 SSU at 100 F., selected from the group consisting of gas oil and mixtures of gas oil and 1 to 25 wt. percent of asphalt, about 4 to 8 wt. percent of finely divided silica having a particle size of about 0.01 to 0.50 micron, and about 5 to 35 wt. percent of a'wood preservative.

wood preservative is powdered borax.

References Cited in the file of this patent UNITED STATES PATENTS Shideler Oct. 20, 1942 Schmitz-I-Iillebricht et a1. June 12, L956 Behr Aug. 14, 1962 

1. A GREASE-LIKE WOOD PRESERVATIVE COMPOSITION CONSISTING OF A MAJOR AMOUNT OF AN OIL BLEND HAVING A VISCOSITY OF 30 TO 40 SSU AT 100*F., WHICH CONSISTS OF GAS OIL CONTAINING IN EXCESS OF 80WT. PERCENT AROMATICS AND HAVING A VISCOSITY OF 20 TO 38 SSU AT 100*F., AND STEAM-CRACKED PETROLEUM TAR; 4 TO 8 WT. PERCENT OF SILCA HAVING PARTICLE SIZE OF 0.015 TO 0.030 MICRON; AND 5 TO 35 WT. PERCENT OF A WOOD PRESERVATIVE. 